Laminated glazing with coloured reflection and high solar transmittance suitable for solar energy systems

ABSTRACT

A laminated and etched glazing unit having a substrate and a multi-layered interference filter each delimited by two main faces; the incident medium having a refractive index n inc =1, the substrate having a refractive index n substrate  defined as: 1.45≤n substrate ≤1.6 at 550 nm, and the exit medium being defined as follows 1.45≤n exit ≤1.6 at 550 nm; and wherein the following requirements are met: The saturation of the colour is higher than 8 at near-normal angle of reflection, except for grey and brown; the visible reflectance is higher than 4%; the variation of the dominant wavelength    MD  of the dominant colour M D  of the reflection is smaller than 15 nm for θ r &lt;60°; and the total hemispherical solar transmittance is above 80%.

FIELD OF THE INVENTION

The invention deals with coloured laminated glazing suitable for solar energy systems offering architectural integration of solar energy systems, e.g. as solar active glass facades.

DEFINITIONS

Direct Transmittance

If parallel beams of radiation incident on a surface, an interface, or a specimen result in transmitted parallel beams, the transmittance is considered as direct. This is the case e.g., for flat surfaces or interfaces.

Diffuse Transmittance

If parallel beams of radiation incident on a surface, an interface, or a specimen result in a more or less wide angular distribution of transmitted beams, the transmittance is considered as diffuse. This is the case e.g., for rough surfaces or interfaces, or for specimens of granular structure. In general, the diffuse transmittance depends on the angle of incidence and the wavelength λ of the radiation. If the angle of incidence is not explicitly mentioned, commonly normal incidence is assumed.

Total Hemispherical Transmittance

The total hemispherical transmittance is obtained by the sum of direct transmittance and diffuse transmittance.

T _(total) =T _(direct) +T _(diffuse)

In general, the total hemispherical transmittance depends on the angle of incidence and the wavelength λ of the radiation. If the angle of incidence is not explicitly mentioned, commonly normal incidence is assumed.

Solar Transmittance T_(sol)

Given a calculated or measured spectrum of the total hemispherical transmittance of a sample T(λ), the solar transmittance T_(sol) is obtained by integration with the solar spectrum I_(sol)(λ):

$T_{sol} = \frac{\int{{{T(\lambda)} \cdot {I_{sol}(\lambda)}}d\; \lambda}}{\int{{I_{sol}(\lambda)}d\; \lambda}}$

where usually the solar spectrum at air mass 1.5 (AM1.5) is employed as intensity I_(sol)(λ).

Visible Reflectance R_(vis)

The visible reflectance R_(vis) is a measure for the brightness of a surface as it appears to the human eye under certain illumination conditions. A white surface or a perfect mirror exhibits 100% visible reflectance, coloured or grey surfaces less. The determination of the visible reflectance R_(vis) is based on the photopic luminous efficiency function V(λ) and depends on the choice of the illuminant I_(ILL)(λ):

$R_{vis} = \frac{\int{{{R(\lambda)} \cdot {I_{ILL}(\lambda)} \cdot {V(\lambda)}}d\; \lambda}}{\int{{{I_{ILL}(\lambda)} \cdot {V(\lambda)}}d\; \lambda}}$

where R(λ) is the simulated or measured hemispherical reflectance of the sample.

Angle of Reflection

With reference to FIG. 29, the angle of reflection θ_(r) is the angle formed by a ray of light reflected from a surface and a line perpendicular to the surface at the point of reflection. Here θ_(l) and θ_(t) correspond respectively to the incidence and transmission angles.

Refractive Index and Extinction Coefficient

When light passes through a medium, some part of it will always be absorbed. This can be conveniently taken into account by defining a complex index of refraction N:

N=n−ik   [1]

where the real part n (refractive index) indicates the phase speed, while the imaginary part k (extinction coefficient) indicates the amount of absorption loss when the electromagnetic wave propagates through the material.

Antireflection

A treated surface is considered as antireflective when the solar transmittance of a light beam at near-normal incidence is higher than for an untreated surface.

CIE 1931 XYZ Colour Space

The International Commission on Illumination (CIE, Commission Internationale d'Eclairage) described how to quantify colours [2]. All existing colours can be represented in a plane and mapped by Cartesian coordinates, as shown in the CIE Chromaticity Diagrams. The quantification is based on the 1931 CIE Colour Matching Functions, x(λ), y(λ), and z(λ), which reflect the colour sensitivity of the human eye. These functions depend to some extent on the width of the observation field (we will use the functions for an opening angle of 2°).

CIE 1976 (L*, a*, b*) Colour Space (Or CIELAB)

CIE L*a*b* is the most complete colour model used conventionally to describe all the colours visible to the human eye. It was developed for this specific purpose by the International Commission on Illumination (Commission Internationale d'Eclairage). The three parameters in the model represent the lightness of the colour (L*, L*=0 yields black and L*=100 indicates white), its position between magenta and green (a*, negative values indicate green while positive values indicate magenta) and its position between yellow and blue (b*, negative values indicate blue and positive values indicate yellow).

Dominant Colour

The dominant wavelength of a colour is defined as the wavelength of the monochromatic stimulus that, when additively mixed in suitable proportions with the specified achromatic stimulus, matches the considered colour stimulus [3]. Thus any colour can be related to a monochromatic dominant colour M_(D) defined by its wavelength λ_(D).

Colour Saturation

The colour saturation is a measurement of how different from pure grey the colour is. Saturation is not really a matter of light and dark, but rather how pale or strong the colour is. The saturation of a colour is not constant, but it varies depending on the surroundings and what light the colour is seen in and is given by:

C* _(ab)=√{square root over ((a*)²+(b*)²)}

where a* and b* are the CIE colour coordinates under daylight illumination CIE-D65.

STATE OF THE ART

The acceptance of solar energy systems as integrated elements of the building's envelope is mainly limited by their unpleasant visual aspect. They are often considered as technical components to be hidden and confined to roof-top applications, where they are less visible and have less impact on the architectural design [4]. The development of better-looking solar systems could open up new perspectives for the architectural integration of solar energy systems, e.g. as solar active glass facades. One solution is to apply a coloured interferential thin film to the inner side of the glazing of the solar system. The coating reflects a colour, thus hiding the technical part of the solar device, but transmits the complementary spectrum. Coloured glass panes based on dielectric thin films multi-depositions have been demonstrated to be of special interest for solar thermal collectors [5-8] and has been the subject to a PCT application in 2004 [9]. The invention disclosed in this PCT application had, however, some weaknesses dealing with:

-   -   The security: the invention considered the use of non-tempered,         non-laminated glazing that did not fulfill the security         requirements for facade installation. Therefore the coloured         designs calculated for single glazing (exit medium air         n_(exit)=1) are not suitable for laminated glazing (exit medium         polymer 1.45≤n_(exit)≤1.6 at 550 nm).     -   The colour stability: in the context of the 2004 PCT         application, the colour was based on quarter wave interference         stacks exhibiting narrow reflection peaks. By limiting the         number of individual layers and choosing the refractive indices         of the involved materials, reasonable amplitudes of the         reflection peak were obtained, thus providing excellent solar         transmittance to the coating. However, as the narrow reflection         peak shifts to smaller wavelength with increasing angle of         reflection, the former developed colours (except blue) were         dependant on the angle of vision/observation/reflection. Example         1 presents a green design which shifted to blue for increasing         angles of observation (see FIG. 1, FIG. 2 and Table 1).     -   The industrial scale production: relatively thick (>100 nm) SiO₂         layers were needed in the coating stacks, thus limiting the         production speed of coloured glasses on industrial scale.

The PCT application also referred to the possibility of applying a surface treatment (hot patterning, acid etching, sand or stone projections . . . ) on the outer side of the collector glazing to in order to create a diffuse light transmittance. This treatment has the effect of reinforcing the masking effect of the solar device technical parts, preventing glare effects and producing mat surfaces that are in high demand in today's architecture. Amongst available diffusive surface treatments, acid etching is undoubtedly the most suitable and most widely used treatment at industrial level. Historically, acidic etching treatments of glasses are performed by using fluoridric-acid-based-solutions [10]. Fluoridric acid is a strong chemical agent responsible of various problems in terms of safety, health of workers and environmental pollution. For this reason, the use of buffered solutions (in which a part of the fluoridric acid is replaced by fluoride salts such as ammonium bifluoride) [11-13] or solutions based on fluoride salts [14-15], less aggressive and more environmentally friendly, are becoming more common.

GENERAL DESCRIPTION OF THE INVENTION

The problems mentioned in the previous chapter have been solved with the present invention which relates to a solar glazing unit as defined in the claims. The present innovation deals with coloured laminated glazing (preferably, but not exclusively, made of glass) with enhanced masking effect, angular colour stability, energetic performances and mechanical stability. The coloured laminated glazing system is schematised in FIG. 3 and can be described as the combination of:

-   -   An encapsulated coloured interferential multi-layered coating,         deposited on the back side of the outer glass (FIGS. 3a and 4a         ), on the back or the front side of a polymeric film which is         encapsulated between two glass panes (FIGS. 3b and 4b ) or on         the front side of the inner glass (FIGS. 3c and 4c ).     -   A textured or non-textured diffusive outer surface     -   An optional anti-reflection coating applied on the back-side of         the inner glass for thermal or PVT applications.

Whereas solar thermal or PVT systems are mounted behind or directly glued to the laminated glazing, PV systems are totally integrated into the laminated glazing.

1. Coloured Coating

The choice of the substrate on which the coloured coating is deposited is of main importance. In order to ensure a maximal efficiency of the solar energy system, the substrate has to present a high solar transmittance, thus limiting the possibilities to solar roll glass, extra-white float glass (very low iron-content) or polymeric materials such as polyethylene terephthalate (PET), polyethylene naphtalate (PEN), fluorocarbon polymer (PFA, FEP, ETFE, PTFE . . . ) and so on. The surface flatness is also a critical issue, especially for facade applications. As no colour variation of the interferential coating should be visible, extra-white float glass and polymer materials, giving more freedom in the choice of the glass nature, are preferred to solar roll glass for the deposition of the coloured coating.

The coloured coating consisting in multilayer interferential stacks of transparent layers has to be of high solar transmittance T_(sol). Thus, as absorption in the coating should be minimised, dielectric oxides are preferably chosen. Among the various possibilities, materials such as SiO₂, Al₂O₃, MgO, ZnO, SnO₂, HfO₂, Nb₂O₅, Ta₂O₅ and TiO₂ are for example perfectly suitable for the invention described here.

The visible reflectance R_(vis) is the percentage of light striking the glazing that is reflected back and provides information on the masking capability of the glazing. This value has then to be high enough to permit a good masking effect of the solar energy system technical parts but low enough to ensure a good solar transmittance. Good compromises have then to be found between masking effect and performances of the solar device. In the context of the invention, R_(vis) has to be higher that 4%.

The intensity of the colour is given by its saturation expressed by:

C* _(ab)=√{square root over ((a*)²+(b*)²)}

where a* and b* are CIE colour coordinates under daylight illumination CIE-D65. In order to provide well-visible colours, the colour saturation has to be higher than 8 at near-normal angle of reflection. Exception is made for grey and brown which correspond respectively to strongly desaturated cold and warm colours.

Concerning the colour stability, improvements have been brought here as compared to the 2004 PCT application by modifying the quaterwave interference stacks in order to get asymmetric designs. The consequence of such modifications is the obtaining of reflectance curves characterised either by a large single reflection peak or by several small reflection peaks. Then, the multilayer coating reflects a colour which is defined, as a function of the shape of the reflectance curve:

-   -   Either by the wavelength of the maximum intensity of a single         reflectance peak situated in the visible part of the solar         spectrum. For example, FIG. 5 represents a reflectance curve at         normal incidence (angle of vision of 0°) with a maximal         intensity at λ_(max)=570 nm which corresponds to a yellow-green         dominant colour for the coating.     -   Or by the combination of the wavelengths of 2 or more         reflectance peaks situated in the visible spectral region. For         example, FIG. 6 shows a reflectance curve at normal incidence         with 3 peaks in the visible part of the spectrum and         respectively situated at 413 nm, 534 nm and 742 nm. The         resultant dominant colour of the considered coating is situated         at λ_(D)=500 nm (green).

With increasing angle of vision most features of the spectra shift to smaller wavelengths, inducing a modification of the position of λ_(max) and thus of the dominant colour of the coating. As example, the reflectance curves obtained for both yellow-green and green coatings at various angles of reflection θ_(r) (from 0° to 85°) are given in FIGS. 7(a) and (b) respectively.

Providing coloured glazing with good angular colour stability is of high importance for building integration. Strong efforts have then been made in order to avoid or limit the colour variations. The principle of the colour stability can be explained as follows. Generally, the colour M of a layer can be regarded as a mixture of several colours whatever the shape of its reflectance curve. For more clarity, the explanations will be given for a fictive coloured layer characterized by two reflection peaks, in the visible part of the solar spectrum, whose wavelengths and colours are respectively λ₁, C₁ and λ₂, C₂ (see FIG. 8a ). The colour M is defined by a dominant colour M_(D) whose wavelength λ_(MD) comprised between λ₁ and λ₂, its position depending on the relative intensity of both reflection peaks (see FIG. 8b ). With increasing angles of vision the reflection peaks shift to shorter wavelengths. The shift of C₁ to C_(1′) has to be compensated by an equivalent shift of C₂ to C_(2′) as well as a modification of the relative intensity of both peaks in order to conserve the position of the point M. At least, the point M has to be kept on the on the colour segment defined by the line MM_(D). In that last case, the dominant colour of the coating remains the same. This compensation can be achieved by choosing carefully the nature and the thickness of the materials of the individual layers constituting the interferential coloured coating stack.

This principle can be extrapolated to more complex designs characterised by more than two peaks of reflection (see FIG. 9).

Green coloured designs based on this principle are given in Examples 2, 3 and 4 (see FIGS. 10, 11, 12, 13, 14, 15 and tables 2, 3 and 4). The (x,y) colour coordinates under CIE-D65 illuminant, the visible reflectance R_(vis), the solar transmittance T_(sol), the dominant wavelength λ_(MD) and colour M_(D) and colour saturation C_(ab)* of those 3 coatings are given for different angles of reflection. Corresponding graphical presentations of colour variations are also shown for each design. For each design, only small variations in colour and in reflectance (especially for θ_(r) up to 60°) are observed in combination with high solar transmittances (above 80% up to 60°). The variation of the wavelength of the dominant colour observed for these coating designs (9 nm of variation between 0° and 60° for Example 2) is almost 4 times lower than for the 2004 PCT application design (Example 1).

Another advantage here as compared to the 2004 PCT application [6], is that the relatively thick SiO₂ coatings have been replaced by other oxides with higher deposition speed. As a matter of facts, multilayer interferential stacks are deposited on industrial scale by in-line magnetron sputtering. For low cost production, the number of sub-layers and the thickness of the individual layers have to be limited.

Other examples of coating designs with various colours in reflection (blue, yellow-green, yellowish-orange, grey and brown) are given in Examples 5 to 9 (see FIGS. 16 to 25 and tables 5 to 9).

2. Diffusive Surface

A diffusive surface treatment is applied on the outer surface of the coloured laminated glazing. The glass substrate can either be extra-white float glass or solar roll glass. Extra-white float glass presents the advantage of having a better flatness and will be preferred for facade applications. Both types of glass are also commercially available with a wide variety of textures and patterns applied on the outer surface. This kind of glass can be used in order to add some relief and get closer to tiles appearance in case of roof applications.

The etching treatment is applied in order to create diffuse light transmittance which reinforces the masking effect of the coloured filter. It also presents the advantage to create mat surfaces often desired by architects and to prevent glare effects.

By choosing appropriate compositions of the etching solution, favourable micro/nano-structures on the treated glass surface can also give rise to anti-reflection properties. For example, the treatment of glass surfaces by acid etching in buffered solutions [13] leads to a particular structure combining micrometric islands with nanometric openings, both uniformly distributed. The resulting low reflectance glass surfaces thus obtained are perfectly suitable for the solar applications described here.

Based on literature [14-15], etching solutions composed of several of the following components have been developed: ammonium bifluoride (ABF), water (H₂O), isopropanol (IPA), sugars (sucrose, fructose, etc.). These solutions are particularly effective over a wide range of compositions and for treatment times lower than 20 minutes.

Examples of effective solutions with range of reasonable concentrations are given below:

-   -   Solution 1: ABF/IPA/water mixture with the following proportions         10-30 wt. %/20-40 wt. %/balance.     -   Solution 2: ABF/sucrose/water mixture with the following         proportions 15-25 wt %/15-40 wt %/balance.

Excellent transmittances are obtained for the treated glass surfaces thanks to anti-reflective properties. The measured hemispherical normal transmittance of the treated glass surfaces is about 95% as regards to 92% for an untreated glass (see FIG. 26).

FIGS. 27(a) and (b) present SEM pictures of glass surfaces respectively structured by an ABF/IPA-based etching solution (ABF/IPA/H₂O=30/10/60) and by an ABF/sucrose-based etching solution (ABF/sucrose/H₂O=18/18/64). Both pictures have been taken for the same etching time (15 min) and at same magnification. In the first case (FIG. 27a ), the surface is relatively smooth and presents some micro-scale protrusions and furrows arising from the junction of nano-holes which are present on the entire surface. In the second case (FIG. 27b ), the surface features a much rougher structure and is densely covered with some kind of pyramids. These pyramids have a height around 10 μm, are defined by different types of polygons as their base area whose dimensions are often around 100 μm to 120 μm and have pronounced nano-structured side walls. The measured gain in solar transmittance can then be explained by anti-reflective properties resulting from micro-scale patterning in combination with a nano-scale roughness modification.

3. Tempering and Lamination

After coating deposition and etching, the different glass panes are tempered. There is no restriction to perform this thermal treatment, as both coloured coatings (made of oxides) and diffusive surfaces (mainly SiO₂) present very good thermal stabilities.

Then, glass panes and if necessary other elements (coated polymeric film, crystalline silicon cells . . . ) are joined together by lamination. Laminating polymers are preferably, but not exclusively elastomer cross-linking products such as EVA (Ethylene-Vinyl-Acetate) or thermoplastic products such as PVB (Polyvinyl Butyral). These products are characterised by high solar transmittances, low refractive indices, and good adhesion to glass or polymer panes.

Both treatments are made and combined in order to fulfill the security requirements for facade applications, but also to provide some advantages. First of all, the lamination can offer the possibility to have different supply chains for coating and etching, depending on the chosen configuration (see FIGS. 3 and 4) thus offering a wide time savings. Moreover the coloured coating is encapsulated, avoiding any colour change due to water condensation on the inner side of the glazing when mounted on thermal collectors.

Another advantage is the good mechanical strength of the laminated glazing which offers:

-   -   The possible use of glazing larger than the solar thermal or PVT         systems which can be directly bonded to the back of the glazing         and thus be completely hidden. Since the coloured coating is         encapsulated, such collectors can be obtained without any colour         change along the glued collector frame (which is the case when         the interferential coating is in direct contact with lamination         polymer or glue). Thermal, PV and PVT systems have therefore         exactly the same external appearance.     -   The possible use of the glass for the mechanical fixation of the         solar devices.

These capabilities allow the production of polyvalent products which provide considerable flexibility for roof and facade installation. As one example, FIG. 28 presents possible variations for the mounting of thermal solar systems glued behind a coloured laminated glazing. In FIG. 28(a), solar thermal collectors are glued on the back of laminated glazing larger than the frame of the collectors. Here the solar collectors are mounted on a roof with glazing overlap and the waterproofing is provided by the presence of seals between two overlapping glazings. Different variations for the mounting of solar thermal collectors in ventilated facade either for residential facade or for large buildings with glass facades are shown respectively in FIGS. 28(b) and (c). Here, the hangers, the overlap wings, the seals and so on can be adaptable to the wishes of the architect, the type and requirements of the building, the local culture of the country, . . . . Same mounting configurations are of course possible for photovoltaic devices, but also for hybrid (combination of thermal and PV devices) roof and facades installations.

4. Optional Anti-Reflection Coating

In order to increase the solar transmittance of solar thermal devices an anti-reflection coating can be applied to the back-side of the inner glass (see FIG. 3).

As a matter of facts, a maximum transmittance value of approximately 92% can be achieved for the best quality glass as a reflectance of 4% on both sides of the glass occurs. By applying an anti-reflection coating characterised by a low refractive index (lower than 1.52) the reflectance of the glass side can be reduced of approximately 3% in the best case.

Ideally, the solar transmittance of the coloured laminated glazing can then increase of approx. 3% and thus compensating the transmittance losses due to the presence of the interferential coloured coating.

REFERENCES

-   [1] H. A. McLeod, Thin Film Optical Filters, American-Elsevier, New     York, 1969. -   [2] International Commission on Illumination CIE, 1986. Colorimetry.     CIE Publication 15.2., 2nd ed., ISBN 3-900-734-00-3, Vienna -   [3] CIE Technical Report (2004) Colorimetry, 3rd ed. Publication     15:2004 -   [4] M. Munari Probst and C. Roecker, “Towards an improved     architectural quality of building integrated solar thermal systems     (BIST),” Solar Energy, vol. 81, September 2007, pp. 1104-1116. -   [5] A. Schüler, C. Roecker, J.-L. Scartezzini, J. Boudaden, I. R.     Videnovic, R. S.-C. Ho, P. Oelhafen,

Sol. Energy Mater. Sol. Cells 84 (2004) 241.

-   [6] J. Boudaden, R. S. C. Ho, P. Oelhafen, A. Schüler, C. Roecker,     J.-L. Scartezzini, Solar Energy Materials & Solar Cells 84, 225     (2004). -   [7] A. Schüler, C. Roecker, J. Boudaden, P. Oelhafen, J.-L.     Scartezzini, Solar Energy 79, 122 (2005). -   [8] A. Schüler, J. Boudaden, P. Oelhafen, E. De Chambrier, C.     Roecker, J.-L. Scartezzini, Solar Energy Materials & Solar Cells 89,     219 (2005). -   [9] A. Schüler, PCT International Publication WO 3004/079278 A1     (2004). -   [10] H. Niederprüm, H. G. Klein, J.-N. Meussdoerffer, U.S. Pat. No.     4,055,458 (1977). -   [11] N. Enjo, K. Tamura, U.S. Pat. No. 4,582,624 (1986). -   [12] G. E. Blonder, B. H. Johnson, M. Hill, U.S. Pat. No. 5,091,053     (1992). -   [13] D. C. Zuel, J.-H. Lin, U.S. Pat. No. 5,120,605 (1992). -   [14] S. H. Gimm, J. H. Kim, U.S. Pat. No. 5,281,350 (1994). -   [15] H. Miwa, U.S. Pat. No. 7,276,181 B2 (2007).

LIST OF FIGURE CAPTIONS

FIG. 1:

Angular dependency of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 1.

FIG. 2:

Reflectance curves of the coating design given in Example 1 for various angles of reflection (from 0° to 85°).

FIG. 3:

Schematic drawings of possible configurations of coloured laminated glazing for thermal and PVT applications. The coloured coating can be deposited (a) on the back side of the outer glass, (b) on one side of a polymeric film which is encapsulated between two glass panes, (c) on the front side of the inner glass.

FIG. 4:

Schematic drawings of possible configurations of coloured laminated glazing for PV applications. The coloured coating can be deposited (a) on the back side of the outer glass, (b) on one side of a polymeric film which is encapsulated between two glass panes, (c) on the front side of the inner glass. Here the technical parts of the PV device are fully integrated into the laminated glazing.

FIG. 5:

1988 C.I.E. normalised photopic luminous efficiency function delimiting the part of the solar spectrum which is visible for the human eye and reflectance curve at normal incidence (angle of vision of 0°) of a yellow-green coating (λ_(max)=570 nm) presenting a single reflection peak.

FIG. 6:

1988 C.I.E. normalised photopic luminous efficiency function delimiting the part of the solar spectrum which is visible for the human eye and reflectance curve at normal incidence (angle of vision of 0°) of a green coating (λ_(D)=500 nm) presenting three reflection peaks in the visible part of the solar spectrum (bulk part of the curve).

FIG. 7:

-   -   (a) Reflectance curves of a yellow-green coating for various         angles of reflection (from 0° to 85°). The reflection peak         situated in the visible part of the spectrum shifts to smaller         wavelengths: λ_(max) varies from λ_(max 0°)=570 nm to         λ_(max 60°)=500 nm leading to a colour change of the coating         from yellow-green to green.     -   (b) Same representation for a green coating design presenting         three reflection peaks in the visible part of the solar         spectrum.

FIG. 8:

-   -   (a) Graphical representation of a fictive reflectance curve         composed by two reflection peaks in the visible part of the         solar spectrum. λ₁, C₁ and λ₂, C₂ are the wavelengths and         colours of the reflectance peaks at low viewing angle. λ_(1′),         C_(1′) and λ_(2′), C_(2′) are the corresponding wavelengths and         colours at higher angle of observation. The dominant colour         M_(D) of the coating is situated at λ_(D) comprised between λ₁         and λ₂, its position depending on the relative intensity of both         reflection peaks.     -   (b) Principle of colour stability represented on the 1931 C.I.E.         chromaticity diagram. M is the resultant colour of a coating         characterised by 2 reflection peaks, in the visible part of the         solar spectrum, defined by C₁ and C₂ at low angle of vision.         C_(1′) and C_(2′) are the corresponding colours for higher angle         of vision. M_(D) is the dominant colour of M.

FIG. 9:

-   -   (a) Graphical representation of a fictive reflectance curve         composed by three reflection peaks in the visible part of the         solar spectrum. λ₁, C₁, λ₂, C₂ and λ₃, C₃ are the wavelengths         and colours of the reflectance peaks at low viewing angle.         λ_(1′), C_(1′), λ_(2′), C_(2′) and λ_(3′), C_(3′) are the         corresponding wavelengths and colours at higher angle of         observation. The dominant colour M_(D) of the coating is         situated at λ_(D) whose position depends on the relative         intensity of all reflection peaks.     -   (b) Principle of colour stability represented on the 1931 C.I.E.         chromaticity diagram. M is the resultant colour of a coating         characterised by 3 reflection peaks, in the visible part of the         solar spectrum, defined by C₁, C₂ and C₃ at low angle of vision.         C_(1′), C_(2′) and C_(3′) are the corresponding colours for         higher angle of vision. M_(D) is the dominant colour of M.

FIG. 10:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 2.

FIG. 11:

Reflectance curves of the coating design given in Example 2 for various angles of reflection (from 0° to 85°).

FIG. 12:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 3.

FIG. 13:

Reflectance curves of the coating design given in Example 3 for various angles of reflection (from 0° to 85°).

FIG. 14:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 4.

FIG. 15:

Reflectance curves of the coating design given in Example 4 for various angles of reflection (from 0° to 85°).

FIG. 16:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 5.

FIG. 17:

Reflectance curves of the coating design given in Example 5 for various angles of reflection (from 0° to 85°).

FIG. 18:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 6.

FIG. 19:

Reflectance curves of the coating design given in Example 6 for various angles of reflection (from 0° to 85°).

FIG. 20:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 7.

FIG. 21:

Reflectance curves of the coating design given in Example 7 for various angles of reflection (from 0° to 85°).

FIG. 22:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 8.

FIG. 23:

Reflectance curves of the coating design given in Example 8 for various angles of reflection (from 0° to 85°).

FIG. 24:

Angular stability of 1931 CIE (x, y) colour coordinates under CIE-D65 illuminant of the coloured design given in Example 9.

FIG. 25:

Reflectance curves of the coating design given in Example 9 for various angles of reflection (from 0° to 85°).

FIG. 26:

Normal hemispherical transmittance measurements of a glass etched by solution 1 (ABF/IPA/H₂O=30/10/60−15 min etch time), a glass etched by solution 2 (ABF/sucrose/H₂O=18/18/64−15 min etch time) and an untreated glass. The normal hemispherical transmittance is around 95% for both etched glasses and around 92% for the untreated glass.

FIG. 27:

SEM pictures of glass surfaces structured by ABF-based etching solutions:

(a) ABF/IPA/H₂O=30/10/60−15 min etch time

(b) ABF/sucrose/H₂O=18/18/64−15 min etch time.

FIG. 28:

Possible variations for the mounting of thermal or PVT solar systems glued behind a coloured laminated glazing: (a) example of roof installation with glazing overlap, (b) example of installation for residential ventilated facade, (c) example of adaptation to large buildings with glass facades.

FIG. 29:

Illustration of the reflection angle θ_(r), incidence angle θ_(l) and transmission angle θ_(t).

EXAMPLES OF COATING DESIGNS Example 1

air//136 nm of L/222 nm of H//glass//222 nm of H/136 nm of L//air

with n_(H)=1.54 and n_(L)=1.8

Example 2

air//glass//30 nm of H/25 nm of L/320 nm of H//polymer

with n_(H)=2.4 and n_(L)=1.65

Example 3

air//glass//185±12 nm of H/25±12 nm of L/35±12 nm of H/35±12 nm of L/130±12 nm of H//polymer

with n_(H)=2.4 and n_(L)=2.0

Example 4

air//glass//160±12 nm of H/130±12 nm of L/65±12 nm of H/25±12 nm of L/70±12 nm of H/160±12 nm of L/100±12 nm of H//polymer

with n_(H)=2.2 and n_(L)=2.0

Example 5

air//glass//45±12 nm of H/70±12 nm of L/45±12 nm of H//polymer

with n_(H)=2.0 and n_(L)=1.65

Example 6

air//glass//175±12 nm of H/85±12 nm of L/50±12 nm of H/25±12 nm of L/300±12 nm of H//polymer

with n_(H)=2.4 and n_(L)=2.0

Example 7

air//glass//120±12 nm of H/120±12 nm of L/95±12 nm of H/90±12 nm of L/90±12 nm of H/95±12 nm of L/100±12 nm of H//polymer

with n_(H)=2.0 and n_(L)=1.65

Example 8

air//glass//40±12 nm of H/75±12 nm of L//polymer

with n_(H)=2.4 and n_(L)=1.65

Example 9

air//glass//50±12 nm of H/90±12 nm of L/65±12 nm of H/55±12 nm of L//polymer

with n_(H)=2.4 and n_(L)=2.0 

1-24. (canceled)
 25. A laminated glazing unit for architectural integration of solar energy systems comprising a substrate delimited by two main faces and a multi-layered interference filter also delimited by two main faces and in contact on one main face with said substrate and on the other main face with a laminating polymer; said substrate being in contact with an incident medium having a refractive index n_(inc)=1 and having a refractive index nine substrate defined as follows: 1.45≤n_(substrate)≤1.6 at 550 nm and; said laminating polymer being the exit medium whose refractive index is defined as follows 1.45≤nexit≤1.6 at 550 nm; and wherein said unit is designed in such a way that the following requirements are met: 1a) The saturation of the colour, given by C*_(ab)=√{square root over ((a*)²+(b*)²)}, according to the CIE colour coordinates L*, a* and b* under daylight illumination CIE-D65 is higher than 8 at normal angle of reflection, except for grey and brown. 1b) The visible reflectance at near-normal angle of reflection R_(vis) is higher than 4%. 1c) The variation of the dominant wavelength λ_(MD) of the dominant colour MD of the reflection with varying angle of reflection θr is smaller than 15 nm for θr<60°. 1d) The total hemispherical solar transmittance at normal incidence is above 80%.
 26. The glazing unit according to claim 25 comprising a light-diffusing rough outer surface on the other main face of the substrate, the light-diffusing rough outer surface being obtained by chemical treatment.
 27. The glazing unit according to claim 25 comprising an acidic etched anti-reflective outer surface on the other main face of the substrate to enhance the optical properties of the system: the solar transmittance of a light beam at normal incidence is approx. 3% higher for the etched surface than for an untreated surface.
 28. The glazing unit according to claim 25 further comprising an anti-reflective coating applied on the back-side of the laminated glazing in order to enhance the optical properties of the system for solar thermal applications: the solar transmittance of a light beam at normal incidence is approx. 3% higher for the surface on which the anti-reflective coating is applied than for an untreated surface.
 29. The glazing unit according to claim 25, wherein the substrate comprises solar roll glass, an extra-white float glass with an iron content <120 ppm or a polymeric material characterised by a solar transmittance higher than 90%.
 30. The glazing unit according to claim 25, wherein the substrate includes a solar roll glass and the solar roll glass surfaces are either flat or textured.
 31. The glazing unit according to claim 25, wherein the laminating polymer comprises an elastomer cross-linking polymer, a thermoplastic product, or an ionoplastic polymer to join glass or polymeric panes together by lamination and the solar transmittance of the unit is higher than 92% for a polymer thickness of 0.4-0.5 mm.
 32. The glazing unit according to claim 25, wherein said multi-layered interference filter is a multilayer interferential stack of up to 9 layers, up to 400 nm physical thickness dielectric layers with low absorption expressed by the extinction coefficient k≤0.2 for wavelengths λ with 450 nm≤λ≤2500 nm.
 33. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter has a green coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 3 sub-layers based on low refractive index material L with 1.4≤nL≤2.2 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the general design being: incident medium air//substrate//30±12 nm of H/25±12 nm of L/320±12 nm of H///exit medium polymer, wherein thickness are physical thicknesses.
 34. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter has a green coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 5 sub-layers based on low refractive index material L with 1.4≤n_(L)≤2.2 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the general design being: incident medium air//substrate//185±12 nm of H/25±12 nm of L/35±12 nm of H/35±12 nm of L/130±12 nm of H//exit medium polymer, wherein thickness are physical thicknesses.
 35. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter has a green coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 7 sub-layers based on low refractive index material L with 1.4≤n_(L)≤2.2 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the general design being: incident medium air//substrate//160±12 nm of H/130±12 nm of L/65±12 nm of H/25±12 nm of L/70±12 nm of H/160±12 nm of L/100±12 nm of H//exit medium polymer, wherein thickness are physical thicknesses.
 36. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter provides a blue coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 3 sub-layers based on low refractive index material L with 1.4≤n_(L)≤1.8 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the multilayer design corresponding hereby to: incident medium air//substrate/45±12 nm of H/70±12 nm of L/45±12 nm of H//exit medium polymer, wherein thickness are physical thicknesses.
 37. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter provides a yellow-green coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 5 sub-layers based on low refractive index material L with 1.65≤n_(L)≤2.1 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the multilayer design corresponding hereby to: incident medium air//substrate/175±12 nm of H/85±12 nm of L/50±12 nm of H/25±12 nm of L/300±12 nm of H//exit medium polymer, wherein thickness are physical thicknesses.
 38. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter provides a yellowish-orange coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 7 sub-layers based on low refractive index material L with 1.4≤n_(L)≤1.8 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the multilayer design corresponding hereby to: incident medium air//substrate/120±12 nm of H/120±12 nm of L/95±12 nm of H/90±12 nm of L/90±12 nm of H/95±12 nm of L/100±12 nm of H//exit medium polymer, wherein thickness are physical thicknesses.
 39. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter provides a grey coloured reflection deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 2 sub-layers based on low refractive index material L with 1.4≤n_(L)≤1.8 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the multilayer design corresponding hereby to: incident medium air//substrate//40±15 nm of H/75±30 nm of L//exit medium polymer, wherein thickness are physical thicknesses.
 40. The glazing unit according to claim 25, wherein the substrate is comprised of glass or a polymer, and said interference filter provides a brown coloured reflection and is deposited on the glass or polymer substrate with 1.45≤n_(substrate)≤1.6 at 550 nm and composed by 4 sub-layers based on low refractive index material L with 1.65≤n_(L)≤2.1 at 550 nm and high refractive index material H with 1.8≤n_(H)≤2.5 at 550 nm; the multilayer design corresponding hereby to:incident medium air//substrate//50±12 nm of H/90±12 nm of L/65±12 nm of H/55±12 nm of L//exit medium polymer, wherein thickness are physical thicknesses.
 41. The glazing unit according to claim 25, further comprising one or more heat treated glass pane(s) for security in facade applications.
 42. A solar energy system comprising a laminated glazing unit according to claim
 25. 43. The solar energy system according to claim 42 comprising a thermal collector and wherein the laminated glazing unit is directly glued to the solar thermal collector.
 44. The solar energy system according to claim 43 wherein the laminated glazing unit is larger than a frame of the thermal collector.
 45. The solar energy system according to claim 42 comprising a photovoltaic system with an active system fully integrated in the laminated glazing unit.
 46. A solar roof or building facade comprising the solar energy system according to claim
 42. 47. The solar roof or building facade according to claim 46 wherein the solar energy system is suspended by fixations attached to the laminated glazing unit.
 48. The solar roof or building facade according to claim 46 including a plurality of laminating glazing units with an overlapping of the laminated glazing units.
 49. The glazing unit according to claim 29, wherein the polymeric material is PET, PEN, PFA, FEP, ETFE, or PTFE.
 50. The glazing unit according to claim 31, wherein the elastomer cross-linking polymer is EVA, or the thermoplastic product is PVB.
 51. The solar energy system according to claim 45, wherein the photovoltaic system with an active system includes silicon cells, photovoltaic thin films, contacts or a back reflector. 